1. Field of the Invention
This invention relates to power transmission belts having cogs spaced along their length on at least one side thereof and having a reinforcing fabric over the cogs. The invention is also directed to a method of forming a belt of this type.
2. Background Art
Cog belts are used on a wide range of machinery and in a wide range of environments. Commonly, these belts are used on systems with variable speed transmissions, such as on snowmobiles, scooters, buggies, and other different types of equipment. These systems may use a drive and driven pulley combination, wherein speed variation is effected by varying the effective diameter of the pulleys.
A typical belt in this environment has a compression rubber layer, a tension rubber layer, cogs with cog troughs and crests alternating along the length of the belt in at least the compression layer, and at least one load carrying cord embedded in a cushion rubber layer. These belts are commonly referred to commercially as raw edge single cog belts or raw edge double cog belts.
In a typical manufacturing process for this type of belt, an unvulcanized rubber sheet, having a length greater than the desired length of the completed belt, is pressed against a plain cogged mold, having alternating grooves and projections, with the rubber heated and under pressure, to form a cog pad. The resulting cog pad has cogs spaced lengthwise at a constant pitch and may have one or more plies of reinforcing fabric thereon. The cog pad is placed on a cylindrical matrix installed on a molding drum having grooves and projections thereon, so that the cog pad meshes with the cylindrical matrix. The cog pad is cut and its ends butt-joined. Load carrying cords are wound around the cog pad followed by another rubber layer and at least one layer of reinforcing fabric. The resulting belt sleeve is then vulcanized.
Typically, the cog pad is cut to length by skilled workers that manually count the number of cogs necessary to produce the desired end belt length and mark a cog trough in chalk where a cut is to be made to produce the desired belt length. The cog pad is severed at cogs at both ends using a cutter.
The unvulcanized rubber sheet is exposed by separating the reinforcing fabric at one end of the cog pad. The reinforcing fabric at the other end of the cog pad is processed to protrude from the other end of the cog pad. The cog pad is then wound around a matrix with grooves and projections and the ends of the rubber layer are butt-joined. The ends of the reinforcing fabric are joined in overlapping relationship. The cog pad is ultimately vulcanized.
However, as seen in FIG. 10, manufacture by this method may result in flaws in the form of creases 10 in reinforcing fabric 11 on the exemplary cog belt 12 shown. The crease 10 is developed at a trough 14 between crests 16 on adjacent cogs 18. At a joint 20 produced by an overlying fabric end portion 22 and an underlying fabric end portion 24, the overlying fabric end portion 22 tends to attract the underlying fabric end portion 24 in the region of the trough 14 during vulcanization. This is attributable to the lack of rubber at the joint 20 in the region of the trough 14. As the belt 12 is operated and the trough 14 is repeatedly bent, cracks may develop at an early stage in the belt life at the trough 14 where the crease 10 is located. This crack may grow and ultimately cause failure of the belt 12.
In one form, the invention is directed to a power transmission belt having an endless body with a length, an inside, and an outside. The body has cogs on at least one of the inside and outside of the body and spaced along the length of the body so as to define alternating cog crests and cog troughs. The cog crests each have oppositely facing side surfaces with an apex between the oppositely facing side surfaces. There is a reinforcing fabric on the at least one of the inside and outside of the body. The reinforcing fabric has first and second spaced end portions with a first free end at the first end portion and a second free end at the second end portion. The first and second end portions overlap so that the first and second free ends are each at a side surface on a cog crest.
In one form, the first and second free ends are each at one of the side surfaces on a first cog.
In one form, the first and second free ends are at the same side surface on the first cog.
In one form, the body has a compression rubber layer and a tension rubber layer and the cogs are formed in at least the compression rubber layer.
In one form, the body comprises at least one cushion rubber layer and at least one load carrying cord embedded in the cushion rubber layer.
In one form, the cogs are formed in a rubber layer, the rubber layer has ends which are mated at a joint, and the joint is at a cog crest.
In one form, the free ends are each at a side surface on a first cog crest and the ends of the rubber layer are mated at the first cog crest.
In one form, the joint is formed at a line and one of the first and second free ends is aligned with the line of the joint.
In one form, there are cogs on the other of the inside and outside of the body that are spaced along the length of the body so as to define alternating cog crests and cog troughs.
In one form, the line of the joint makes an angle with a lengthwise line through the body that is equal to 60-90xc2x0. The angle may be between 65 and 80xc2x0.
In one form, the first and second end portions are overlapped at the apex of a cog crest.
In one form, the body has a rubber layer and there are short reinforcing fibers in the rubber layer. This rubber layer may define at least part of a compression section.
In one form, there are short reinforcing fibers in the cushion rubber layer.
In one form, the reinforcing fabric consists of at least one of a) cotton fibers, b) polyester fibers, and c) nylon fibers.
In one form, the reinforcing fabric is made by one of a) plain weaving, b) twill weaving, and c) sateen weaving.
In one form, the reinforcing fabric has warp and weft yarns crossing at an angle of 90-120xc2x0.
In one form, the reinforcing fabric is treated with an RFL solution and friction coated with a rubber composition.
The invention is further directed to a method of forming a power transmission belt/belt sleeve including the steps of: placing a reinforcing fabric against an unvulcanized rubber layer; forming the reinforcing fabric and unvulcanized rubber layer against a mold surface having alternating grooves and projections to produce a cog pad having first and second spaced ends and cog crests and troughs alternating between the first and second spaced ends, each cog crest having oppositely facing side surfaces with an apex between the oppositely facing side surfaces; processing the cog pad at the first end of the cog pad so that a part of the fabric layer projects beyond the rubber layer at the first end of the cog pad; processing the reinforcing fabric at the second end of the cog pad to expose the rubber layer; joining the rubber layer at the first and second ends of the cog pad; overlapping the part of the reinforcing fabric at the first end of the cog pad with the reinforcing fabric at the second end of the cog pad so that a) a free end of the part of the reinforcing fabric at the first end of the cog pad is at a side surface on a cog crest and b) a free end of the reinforcing fabric at the second end of the cog pad is on a cog crest; and combining the cog pad with at least one additional component to define a power transmission belt/belt sleeve having a length.
The step of combining the cog pad with at least one other component may involve combining the cog pad with at least one cushion rubber layer and at least one load carrying cord extending lengthwise of the body and embedded in the cushion rubber layer.
In one form, the rubber layer is a compression rubber layer and the step of combining the cog pad with at least one other component involves combining the cog pad with a tension rubber layer.
The step of joining the rubber layer may involve placing the cog pad around a mold with alternating grooves and projections and joining the rubber layer at the first and second ends with the cog pad placed around the mold.
The method may further include the step of vulcanizing the cog pad with at least one additional component.
The method may further include the step of cutting the power transmission belt/belt sleeve to define a plurality of power transmission belts.
The method may further include the step of forming the reinforcing fabric by one of a) plain weaving, b) twill weaving, and c) sateen weaving.
The step of joining the rubber layer may involve mating ends of the rubber layer at the first and second ends of the cog pad to produce a joint at a cog crest.
The step of joining the rubber layer may involve mating ends of the rubber layer at the first and second ends of the cog pad to produce a joint line that is at an angle of 60-90xc2x0 to a line extending between the first and second ends of the cog pad. The angle may be between 65 and 80xc2x0.
In one form, the free end of the part of the reinforcing fabric at the first end of the cog pad and the free end of the reinforcing fabric at the second end of the cog pad are on the same cog crest.
In one form, the free end of the part of the reinforcing fabric at the first end of the cog pad and the free end of the reinforcing fabric at the second end of the cog pad are on the same side surface on the same cog crest.
In one form, the free end of the part of the reinforcing fabric at the first end of the cog pad and the free end of the reinforcing fabric at the second end of the cog pad are on different side surfaces on the same cog crest.
The invention is further directed to a method of forming a power transmission belt including the steps of: placing a reinforcing fabric against an unvulcanized rubber layer; forming the reinforcing fabric and unvulcanized rubber layer against a mold surface having alternating grooves and projections to produce a cog pad having first and second spaced ends and cog crests and troughs alternating between the first and second spaced ends, each cog crest having oppositely facing side surfaces with an apex between the oppositely facing side surfaces; processing the cog pad at the first end of the cog pad so that a part of the fabric layer projects beyond the rubber layer at the first end of the cog pad; joining the rubber layer at the first and second ends of the cog pad; overlapping the part of the reinforcing fabric at the first end of the cog pad with the reinforcing fabric at the second end of the cog pad so that a) a free end of the part of the reinforcing fabric at the first end of the cog pad is at a side surface on a cog crest and b) a free end of the reinforcing fabric at the second end of the cog pad is on a cog crest; and combining the cog pad with at least one additional component to define a power transmission belt/belt sleeve having a length.
The step of combining the cog pad with at least one other component may involve combining the cog pad with at least one cushion rubber layer and at least one load carrying cord extending lengthwise of the body and embedded in the cushion rubber layer.
In one form, the rubber layer is a compression rubber layer and the step of combining the cog pad with at least one other layer involves combining the cog pad with a tension rubber layer.
The step of joining the rubber layer may involve placing the cog pad around a mold with alternating grooves and projections and joining the rubber layer at the first and second ends with the cog pad placed around the mold.
The method may further include the step of vulcanizing the cog pad with at least one additional component.
The method may further include the step of cutting the power transmission belt/belt sleeve to define a plurality of power transmission belts.
The method may further include the step of forming the reinforcing fabric to be flush with the second end of the cog pad.
The step of joining the rubber layer may involve mating ends of the rubber layer at the first and second ends of the cog pad to produce a joint at a cog crest.
The step of joining the rubber layer may involve mating ends of the rubber layer at the first and second ends of the cog pad to produce a joint line that is at an angle of 60-90xc2x0 to a line extending between the first and second ends of the cog pad. The angle may be between 65 and 80xc2x0.
In one form, the free end of the part of the reinforcing fabric at the first end of the cog pad and the free end of the reinforcing fabric at the second end of the cog pad are on the same cog crest.
In one form, the free end of the part of the reinforcing fabric at the first end of the cog pad and the free end of the reinforcing fabric at the second end of the cog pad are on the same side surface on the same cog crest.
In one form, the free end of the part of the reinforcing fabric at the first end of the cog pad and the free end of the reinforcing fabric at the second end of the cog pad are on different surfaces on the same cog crest.